Couplings and transition fittings of the type having a gripping member are well known, see for example Applicants U.S. Pat. No. 5,593,186. In general these couplings include a nut, body, gripping member having a plurality of inwardly directed barbed projections, as well as a sub-assembly of a compression sleeve and resilient gasket ring that is typically permanently attached to the inner end of the compression sleeve. The nut and the gripping member include abutting tapered surfaces. A pipe end is freely insertable through the sub-assembly and into a socket in the body of the coupling. As the nut is tightened it exerts both a radial and longitudinal force on the grip ring that in turn longitudinally exerts a force on the sleeve and gasket ring. The gasket ring encounters an abutment in a socket in the body, and further tightening of the nut then further radially compresses the gripping member so that its inwardly directed barbed projections engage the outer surface of a pipe to which the coupling is attached. There may also be provided abutment surfaces within the body of the coupling and the nut that abut inner and outer surfaces of a flange outstanding from the outer end of the compression sleeve.
One skilled in the art will appreciate that as the nut is tightened, the tapered surface of the nut acts upon the tapered surface of the gripping member causing it to be both compressed and urged into the body. As the gripping member engages the pipe it is also drawn into the assembly.
Whilst this works well on plastic pipes, it does not work well on metal pipes because the gripping ring, itself made of plastic material, does not possess sufficient strength or hardness to engage a metal pipe. Annular plastic barbs simply can not engage metal pipes with sufficient resilience and even under a small longitudinal force on the pipe, the pipe generally disengages from the coupling.
To overcome this problem, it has been known to modify the gripping member to include protruding metal strips or teeth (generally stainless steel) extending longitudinally along the pipe. However, these modified gripping members are not suitable for plastic pipes since the plastic is easily damaged and cut by the protruding strips. Further, the softer the material, the greater the surface contact required between the gripping members projections and the pipe so that in soft pipes the so modified gripping members are generally unsuitable.
The main object of this invention is therefore to overcome the abovementioned problems or at least provide the public with a useful alternative by providing improvements whereby the body, nut and gripping member (compression ring) form a preliminary assembly through which can be inserted either a metal or a plastic pipe, which is secured by tightening the nut, or removed by unscrewing the nut.